Method of Controlling a Fabrication Process Using an Iso-Dense Bias

ABSTRACT

Embodiments of controlling a fabrication process using an iso-dense bias are generally described herein. Other embodiments may be described and claimed.

FIELD OF THE INVENTION

The field of invention relates generally to optical metrology and, moreparticularly, to the use of optical metrology to monitor one or moreoutput parameters from an upstream process or processes and providingfeedback to adjust the output parameters from the upstream process orprocesses.

BACKGROUND INFORMATION

Periodic gratings are typically used for process monitoring and controlin the field of semiconductor manufacturing. The periodic gratings maybe one or more lines fabricated in series on a workpiece. For example,one typical use of periodic gratings includes fabricating a periodicgrating in proximity to the operating structure of a semiconductingchip. The periodic grating is then illuminated with an electromagneticradiation by an optical metrology tool. The electromagnetic radiationthat deflects off of the periodic grating are collected as a diffractionsignal. The diffraction signal is then analyzed to determine whether theperiodic grating, and by extension whether the operating structure ofthe semiconductor chip, has been fabricated according to specifications.

In one conventional system, the diffraction signal collected fromillumination of the periodic grating (the measured diffraction signal)is compared to a library of simulated diffraction signals. Eachsimulated diffraction signal in the library is associated with ahypothetical profile. When a match is made between the measureddiffraction signal and one of the simulated diffraction signals in thelibrary, the hypothetical profile associated with the simulateddiffraction signal is presumed to represent the actual profile of theperiodic grating.

The actual profile of the periodic grating may represent a series offeatures with very tightly controlled parameters, or criticaldimensions. The critical dimension may be a line width, a space width,or a contact length. The series of features may be tightly arranged indense regions and loosely arranged in isolated regions. The combinationof at least one dense region and at least one isolated region is arepeating structure. A diffraction signal measured from a feature in anisolated region may be very different from a diffraction signal measuredfrom a similarly-sized feature in a dense region.

The diffraction signal measured from an isolated structure in anisolated region is used to determine an isolated structure criticaldimension (ICD). The diffraction signal measured from a dense structurein a dense region is used to determine a dense structure criticaldimension (DCD). The difference between the isolated structure criticaldimension (ICD) and the dense structure critical dimension (DCD) isknown as the iso-dense bias (Δ_(IB)),

Δ_(IB)=ICD−DCD

The iso-dense bias is accounted for by the optical metrology tool sothat similarly sized features may be measured consistently, independentof surrounding features. Currently, the iso-dense bias is determined bymaking at least one measurement of features in a dense region and asecond measurement of features in an isolated region to find adifference between the isolated structure critical dimension (ICD) andthe dense structure critical dimension (DCD). This requires consecutivemeasurements of at least one metrology grating target with isolated anline and one grating target with dense lines. The iso-dense bias isrepresented by the difference between these measurements. Calculatingthe iso-dense bias using this methodology requires multiple,time-consuming measurements by the optical metrology tool.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and not as alimitation in the figures of the accompanying drawings, in which

FIG. 1 is an illustration of the use of optical metrology to measurediffracted spectra from a grating layer;

FIG. 2A illustrates a measured diffracted spectrum graph compared todiffracted spectra graphs of instances in a profile library;

FIG. 2B illustrates a structure profile of a measured periodic structurecompared to profiles of instances in a profile library;

FIG. 3 is an illustration of a top view of one embodiment of a hybridgrating profile;

FIG. 4 is an illustration of a side view of the hybrid grating profileof FIG. 3;

FIG. 5 is an illustration of a top view of an embodiment of an array ofembedded elements formed as a hybrid grating profile as part of thewafer;

FIG. 6 is an illustration of a side view of the hybrid grating profileof FIG. 5;

FIG. 7 is an illustration of another embodiment of a hybrid gratingprofile;

FIG. 8 is an illustration of a side view of the hybrid grating profileof FIG. 7;

FIG. 9 is a table of measurement data of an isolated line-space profileand a dense line-space profile;

FIG. 10 is a table of measurement data of a hybrid grating profile;

FIG. 11 is an exemplary block diagram of an optical metrology systemcoupled to a fabrication cluster; and

FIG. 12 is a flowchart describing one embodiment of a method of usingoptical metrology to monitor one or more output parameters from anupstream process or processes and providing feedback to adjust theoutput parameters from the upstream process or processes.

DETAILED DESCRIPTION

A method of using optical metrology to monitor one or more outputparameters from an upstream process or processes and providing feedbackto adjust output parameters from the upstream process or processes isdisclosed in various embodiments. However, one skilled in the relevantart will recognize that the various embodiments may be practiced withoutone or more of the specific details, or with other replacement and/oradditional methods, materials, or components. In other instances,well-known structures, materials, or operations are not shown ordescribed in detail to avoid obscuring aspects of various embodiments ofthe invention. Similarly, for purposes of explanation, specific numbers,materials, and configurations are set forth in order to provide athorough understanding of the invention. Nevertheless, the invention maybe practiced without specific details. Furthermore, it is understoodthat the various embodiments shown in the figures are illustrativerepresentations and are not necessarily drawn to scale.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, material, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the invention, but do not denote that theyare present in every embodiment. Thus, the appearances of the phrases“in one embodiment” or “in an embodiment” in various places throughoutthis specification are not necessarily referring to the same embodimentof the invention. Furthermore, the particular features, structures,materials, or characteristics may be combined in any suitable manner inone or more embodiments. Various additional layers and/or structures maybe included and/or described features may be omitted in otherembodiments.

Various operations will be described as multiple discrete operations inturn, in a manner that is most helpful in understanding the invention.However, the order of description should not be construed as to implythat these operations are necessarily order dependent. In particular,these operations need not be performed in the order of presentation.Operations described may be performed in a different order than thedescribed embodiment. Various additional operations may be performedand/or described operations may be omitted in additional embodiments.

There is a general need to monitor one or more output parameters from anupstream process or processes and provide feedback to adjust processparameters and/or equipments settings of the upstream process orprocesses. An example of an output parameter that may be used forprocess monitoring is iso-dense bias. A change in iso-dense bias may beused to detect changes in output produced by an upstream process or by aseries of upstream processes. One embodiment of a method of controllinga fabrication process using iso-dense bias comprises forming a gratinglayer on a workpiece using the fabrication process, providing theworkpiece with the grating layer comprising a plurality of repeatingprofiles to a metrology tool, each repeating profile comprising a denseregion and an isolated region, the dense region comprising a pluralityof features including a comparison structure, the isolated regionincluding an isolated structure, the plurality of features in the denseregion and the isolated feature in the isolated region configured in apattern such that an iso-dense bias between the isolated feature and thedense feature is within a range determined for the workpiece. Thegrating layer is exposed to electromagnetic energy and a diffractionsignal is measured from the electromagnetic energy diffracted by thegrating layer and an iso-dense bias is determined. The iso-dense bias istransmitted to a fabrication cluster wherein the fabrication cluster wasused to create the grating layer on the workpiece, the fabricationcluster having a plurality of process parameters and equipment settings.One or more process parameters or equipment settings of the fabricationcluster are adjusted based at least on the iso-dense bias.

FIG. 1 is an illustration of the use of an optical metrology system tomeasure the diffracted spectra from a grating layer. The opticalmetrology system 40 consists of a metrology beam source 41 projecting abeam 43 at the hybrid grating profile 59 of a workpiece or wafer 47mounted on a metrology platform 55. The beam 43 is projected at anincidence angle theta (θ) towards the hybrid grating profile 59. Thediffracted beam 49 is measured by a beam receiver 51. The diffractedbeam data 57 is transmitted to a metrology profiler system 53. Themetrology profiler system 53 compares measured diffracted beam data 57,or measured diffraction signal against a library of simulated diffractedbeam data, or simulated diffraction signal representing varyingcombinations of profile parameters of the hybrid grating profile 59 andresolution.

The optical metrology system 40 is configured to determine one or moreprofile parameters of a hybrid grating profile 59 using any number ofmethods which provide a best matching simulated diffraction signal to ameasured diffraction signal. These methods can include a library-basedprocess, or a regression based process using simulated diffractionsignals obtained by applying Maxwell's equations and using a numericalanalysis technique to solve Maxwell's Equations, such as rigorouscoupled wave analysis (RCWA) and machine learning systems. For adiscussion, see U.S. Pat. No. 6,891,626, titled CACHING OF INTRA-LAYERCALCULATIONS FOR RAPID RIGOROUS COUPLED-WAVE ANALYSES, filed on Jan. 25,2001, issued May 10, 2005, which is incorporated herein by reference inits entirety. The simulated diffraction signal may also be generatedusing a machine learning system (MLS) employing a machine learningalgorithm, such as back-propagation, radial basis function, supportvector, kernel regression, and the like. See, U.S. Patent PublicationNo. US 2004-0267397 A1, titled OPTICAL METROLOGY OF STRUCTURES FORMED ONSEMICONDUCTOR WAFERS USING MACHINE LEARNING SYSTEMS, filed on Jun. 27,2003, which is incorporated herein by reference in its entirety. Seealso, U.S. Pat. No. 6,943,900, titled GENERATION OF A LIBRARY OFPERIODIC GRATING DIFFRACTION SIGNALS, filed on Jul. 16, 2001, issuedSep. 13, 2005, which is incorporated herein by reference in itsentirety; U.S. Pat. No. 6,785,638, titled METHOD AND SYSTEM OF DYNAMICLEARNING THROUGH A REGRESSION-BASED LIBRARY GENERATION PROCESS, filed onAug. 6, 2001, issued Aug. 31, 2004, which is incorporated herein byreference in its entirety; and U.S. Pat. No. 6,891,626, titled CACHINGOF INTRA-LAYER CALCULATIONS FOR RAPID RIGROUS COUPLED-WAVE ANALYSES,filed on Jan. 25, 2001, issued May 10, 2005, which is incorporatedherein by reference in its entirety.

The library instance best matching the measured diffracted beam data 57is selected. The profile and associated critical dimensions of theselected library instance correspond to the cross-sectional profile andcritical dimensions of the features of the hybrid grating profile 59.The optical metrology system 40 may utilize a reflectometer, anellipsometer, or other optical metrology device to measure thediffracted beam or spectrum.

FIG. 2A illustrates a measured diffracted spectrum graph compared todiffracted spectra graphs of instances in a profile library. Thewavelength in nanometers (nm) is shown in the X-axis and cosine delta(Δ), an ellipsometric measurement of the diffracted spectrum, in theY-axis. A profile library is created with ranges of CD's and otherprofile parameters of structures in a wafer. The number of instances ofthe profile library is a function of the combinations of the variousCD's and other profile parameters at the specified resolution. Forexample, the range of the top CD for the dense lines and the isolatedlines of the hybrid grating may vary from 40 to 80 nm and the specifiedresolution is 0.5 nm. In combination with the other profile parametersof the structure, one or more instances of the profile library arecreated starting at 40 nm top CD and for every, 0.5 nm incrementthereafter until 80 nm. For example, instances of a profile library fortrapezoidal profiles may have diffracted spectra and profile parametersincluding a top CD, a bottom CD, and height. In FIG. 2A, a first libraryspectrum 63 representing a set of the profile parameters at a givenresolution and a second library spectrum 65 with a different set ofprofile parameters at the same resolution are illustrated. A measureddiffracted spectrum 61 is in close proximity to library spectra 63 and65. One aspect of the present invention is to determine the profilemodel of an optical digital profilometry model that corresponds to themeasured diffracted spectrum 61 based on the measured diffractedspectrum 61 and on known values in the profile library.

FIG. 2B illustrates a structure profile of a measured periodic structurecompared to profiles of instances in a profile library. A first libraryprofile 71 of a trapezoidal structure is illustrated with a secondlibrary profile 75. A measured diffracted spectrum corresponds to aprofile 73, shown as a dotted line, with profile parameters that are inclose proximity to library profiles 71 and 75. As an example, assumethat the first library profile 71 corresponds to the first libraryspectrum 63 and that the second library profile 75 corresponds to thesecond library spectrum 65. As depicted in FIG. 2A, neither libraryspectrum 63 or 65 exactly matches the measured diffracted spectrum 61.As such, in most conventional systems, based on a “best match”algorithm, either library spectrum 63 or 65 would be selected as theclosest match. However, this results in a certain amount of error. Forexample, assume that the second library spectrum 65 is selected as amatch for measured diffracted spectrum 61. In that case, the secondlibrary profile 75 is selected as representing the actual profile of theperiodic grating.

However, as depicted in FIG. 2B, there is a difference/error between thesecond library profile 75 and the actual profile of the periodic grating(i.e., the profile 73). One solution may be to increase the resolutionof the library so that there would be a library spectrum that moreclosely matches the measured spectrum. However, this increases the sizeof the library, which has the disadvantage of more time and computationto generate the library, to store the library, and to search thelibrary.

FIG. 3 is an illustration of a top view of one embodiment of repeatingfeatures formed as a hybrid grating profile 59 as part of the wafer 47in FIG. 1. A first reference grating 300 is one embodiment of the hybridgrating profile 59 that is comprised of a series of dense featuresadjacent to an isolated line structure 335, separated by a largeseparation 310. In this embodiment, a combination of a plurality ofdense features comprising a comparison line structure 345 and anisolated feature comprising at least one isolated line structure 335creates a hybrid grating profile 59.

In one embodiment, a dense structure 315 is separated from a comparisonline structure 345 by a narrow space 325 to form a dense feature. Thenarrow space 325 may have a narrow space width 330 that is equal to orup to two times as large as a comparison line structure width 350,though the embodiment is not so limited. In one embodiment, thecomparison line structure width 350 ranges approximately between 15 and200 nm. In another embodiment, the comparison structure width rangesapproximately between 50 and 100 nm. For example, the comparison linestructure width 350 may range approximately between 60 and 90 nm and thenarrow space width may range approximately between 90 and 120 nm.

A dense structure width 320 may be approximately equal to or larger thanthe comparison line structure width 350. In one embodiment, the densestructure width 320 may range approximately between 15 and 1000 nm. Inanother embodiment, the dense structure width 320 may rangeapproximately between 200 and 700 nm. For example, the dense structurewidth 320 may range approximately between 400 and 500 nm.

The comparison line structure width 350 may also be approximately equalto or narrower than an isolated line structure width 340. For example,the isolated line structure width 340 may range approximately between 50and 400 nm. In another example, the isolated line structure width 340may range approximately between 100 and 200 nm. Also, a distance betweenthe isolated line structure 335 and the comparison line structure 345should exceed a coherence length of an optical stepper or scanner, whichis defined by an illumination wavelength, a numerical aperture and acoherence parameter (σ_(i)).

The comparison structure may be surrounded by a plurality of densestructures 315, as shown in FIG. 3. However, the order and shape ofdense structures 315, comparison line structures 345, and narrow spaces325 may differ from the embodiment shown in FIG. 3. Critical dimensionsof features may be in the form of structures, they may be in the form ofspaces between the structures, or they may be some combination offeatures thereof. As an example, the comparison line structure width350, the isolated line structure width 340, the narrow space width 330,and the dense structure width 320 may each be critical dimensions.

The isolated line structure 335 may be a line, a rectangle, or someother geometric shape or some variant thereof, though the embodiment isnot so limited. The separation 310 may have a separation width 355 thatis two to four times as large as an isolated line structure width 340.The dense structure 315, the comparison line structure 345, and theisolated line structure 335 may be separated from a neighboringstructure 360 by a gap width 365 wherein the gap width 365 is equal toor greater than the separation width 355. In one embodiment, it ispreferred to provide a separation width 355 that is equal to orapproximately equal to the gap width 365.

In one embodiment, to avoid optical proximity effects, a dense featureoffset 370 measured from a midpoint of the comparison line structure 345to a distal edge of the dense structure 315, and an isolated featureoffset 375 measured from a midpoint of the isolated line structure 335to a neighboring structure 360 as shown in FIG. 3 are each greater thana coherence diameter of a lithography system used to define a pluralityof structures comprising the comparison line structure 345 and the densestructure 315. A range determined for the workpiece, in one embodiment,may mean that the dense feature offset 370 measured from a midpoint ofthe comparison line structure 345 to a distal edge of the densestructure 315, and the isolated feature offset 375 measured from amidpoint of the isolated line structure 335 to a neighboring structure360 as shown in FIG. 3 are each equal to or up to two times greater thanthe coherence diameter of the lithography system used to define aplurality of structures comprising the comparison line structure 345 andthe dense structure 315. In another embodiment, the dense feature offset370 and the isolated feature offset 375 are each equal to or up to 5times greater than the coherence diameter of the lithography system usedto define a plurality of structures comprising the comparison linestructure 345 and the dense structure 315.

The coherence diameter (d_(wafer)) is defined according to basicprinciples of optical lithography imaging, as the wavelength (λ) of anillumination source divided by a coherence parameter (σ) and a waferside numerical aperture of the scanner lens (NA_(wafer)), expressed as:

$d_{wafer} = \frac{\lambda}{\sigma \cdot {NA}_{wafer}}$

Wherein the coherence parameter (σ) is a ratio of the numerical apertureof the illumination source NA_(illu) and the mask side numericalaperture of the scanner lens NA_(mask), expressed as:

$\sigma = \frac{{NA}_{illu}}{{NA}_{mask}}$

Design of a hybrid grating profile 59, illustrated in FIG. 3 throughFIG. 8 should be performed to avoid optical proximity effects, asdiscussed supra.

A mask design of the hybrid grating profile 59 is determined by printingconditions and other processing conditions. For example, a positiveresist process would require a positive mask whereas a negative resistprocess would require a negative mask. In order to print a mask patternof FIG. 4 onto a wafer, a negative resist process would require a tonereversal. In another embodiment, a pattern is printed that is thereverse of FIG. 4, i.e., lines become spaces and vice versa. In thiscase, the mask has to be reversed correspondingly. The feature sizes,including any critical dimensions on the mask are defined by thetargeted feature sizes on the wafer and by the reduction ratio (ex. 4:1for DUV Lithography). Resolution enhancement techniques such as phaseshifting masks (PSM), Optical Proximity Correction (OPC) features andDouble Patterning Lithography (DPL) may be applied for the design of thehybrid mask to insure the correct printing of critical features.

FIG. 4 is an illustration of a side view of the hybrid grating profile59 of FIG. 3. The first reference grating 300 may comprise an isolatedline structure 335, a comparison line structure 345, a dense structure315, and a base layer 460 on a substrate 470. The substrate 470 maycomprise silicon, strained silicon, gallium arsenide, gallium nitride,silicon germanium, silicon carbide, carbide, diamond, and/or othermaterials such as a buried insulating layer. The base layer 460 may be adoped or undoped epitaxial layer, a bottom anti-reflective coatinglayer, a resist layer, or a hard mask layer comprising silicon oxide,silicon nitride or silicon oxynitride formed on the substrate 470 usingmethods known to one skilled in the art. The base layer 460 may becomprised of a single material or the base layer 460 may be a pluralityof layered and unpatterned or patterned films. The plurality of densestructures 315, at least one comparison line structure 345, and at leastone isolated line structure 335 may be formed on the base layer 460 or,alternatively, on the substrate 470 from one or more resist,anti-reflective coating, silicon nitride, or silicon oxide layers usingmethods known to one skilled in the art.

Each structure width and height, for example an isolated structureheight 410, including the dense structure 315, isolated line structure335, comparison line structure 345 and the separation 310 and narrowspace 325 may each be characterized as critical dimensions. The locationof the critical dimension of a structure may be at a bottom location 420proximal to the base layer 460, a top location 440 distal from the baselayer 460, or at some intermediate location 430 between the bottomlocation 420 and the top location 440. A sidewall angle 450 of eachstructure may also be a critical dimension. An iso-dense bias is derivedas a difference between a determined critical dimension for the isolatedline structure 335 and a determined critical dimension for thecomparison line structure 345. Determining a critical dimension is theresult of a determination process using regression, libraries, and/ormachine learning systems and the measured diffraction signal ordiffracted spectrum. In one embodiment, the iso-dense bias is thedifference between the isolated line structure width 340 measured at thetop location 440 and the comparison line structure width 350 measured atthe top location 440 from a two dimensional perspective. In anotherembodiment, the iso-dense bias is the difference between the isolatedline structure width 340 at the intermediate location 430 and thecomparison line structure width 350 at the intermediate location 430 ina three dimensional manner, though the embodiment is not so limited.

FIG. 5 is an illustration of a top view of an embodiment of an array ofembedded elements formed as a hybrid grating profile 59 as part of thewafer 47 in FIG. 1. The second reference grating 500 is anotherembodiment of the hybrid grating profile 59 that is comprised of aseries of dense elements adjacent to an isolated element 535, separatedby a large form 510. In this embodiment, a dense element 515 isseparated from a comparison element 545 by a narrow form 525 to create adense feature. The narrow form 525 may have a narrow form width 530 thatis approximately two times as large as a comparison structure width 550,though the narrow form 525 may be smaller than the comparison elementwidth 550. A dense form width 520 may be approximately equal to orlarger than the comparison element width 550. The comparison elementwidth 550 may be approximately equal to an isolated element width 540.The comparison element width 550 and the isolated element width 540 maybe critical dimensions. In another embodiment, the comparison elementwidth 550 is within 20%, smaller or larger, of the isolated elementwidth 540. The comparison element width 550 may also be a criticaldimension. The comparison structure may be surrounded by a plurality ofdense elements 515, as shown in FIG. 3. However, the order and shape ofdense elements 515, comparison elements 545, and narrow forms 525 maydiffer from the embodiment shown in FIG. 3.

In an alternate embodiment, an isolated element may be a circularisolated element 560 and a comparison element may be a circularcomparison element 565. However, the shape of the isolated element andthe comparison element may be another geometric shape or some variantthereof.

FIG. 6 is an illustration of a side view of the hybrid grating profileof FIG. 5. The first reference grating 500 may comprise an isolatedelement 535, a comparison element 545, a dense element 515, and a baselayer 460 on a substrate 470. The substrate 470 may comprise silicon,strained silicon, gallium arsenide, gallium nitride, silicon germanium,silicon carbide, carbide, diamond, and/or other materials such as aburied insulating layer. The base layer 460 may be a doped or undopedepitaxial layer, a bottom anti-reflective coating layer, a resist layer,or a hard mask layer comprising silicon oxide, silicon nitride orsilicon oxynitride formed on the substrate 470 using methods known toone skilled in the art. The plurality of dense elements 515, at leastone comparison element 545, and at least one isolated element 535 may beformed on the base layer 460 or, alternatively, on the substrate 470from one or more resist, anti-reflective coating, silicon nitride, orsilicon oxide layers using methods known to one skilled in the art.

Each element width and depth including the dense element 515, isolatedelement 535, comparison element 545 and the large form 510 and narrowform 525 may each be characterized as critical dimensions. The locationof the critical dimension of a structure may be at a bottom location 620proximal to the base layer 460, a top location 640 distal from the baselayer 460, or at some intermediate location 630 between the bottomlocation 620 and the top location 640. A sidewall angle of eachstructure may also be a critical dimension. An iso-dense bias iscalculated as a difference between a determined critical dimension forthe isolated element 535 and a determined critical dimension for thecomparison element 545. In one embodiment, the iso-dense bias is thedifference between the isolated element width 540 measured at the toplocation 640 and the comparison element width 550 measured at the toplocation 640 in a two dimensional manner. In another embodiment, theiso-dense bias is the difference between the isolated element width 540at the intermediate location 630 and the comparison element width 550 atthe intermediate location 630 in a three dimensional manner, though theembodiment is not so limited.

FIG. 7 is an illustration of another embodiment of a hybrid gratingprofile 59 as part of the wafer 47 in FIG. 1. A third reference grating700 is one embodiment of the hybrid grating profile 59 that is comprisedof a plurality of isolated vias 720 located proximate to a plurality ofdense vias 760. In this embodiment, a combination of at least one densevia 760 and at least one isolated via 720 creates a hybrid gratingprofile 59.

In this embodiment, each isolated via 720 is square and approximatelythe same size and shape in this embodiment. In another embodiment, oneor more isolated vias 720 may be unique in size and/or shape. Further inthis embodiment, each isolated via 720 formed in an isolated via field730 extends through the isolated via field 730 to a base layer 460.However, the isolated via 720 may be partially formed such that a bottomof the isolated via is situated along a depth of the isolated via field730. The base layer 460 and/or the isolated via field 730 may be a dopedor undoped epitaxial layer, a bottom anti-reflective coating layer, aresist layer, or a hard mask layer comprising silicon oxide, siliconnitride or silicon oxynitride formed on the substrate 470 using methodsknown to one skilled in the art.

A plurality of dense vias 760 are formed nearby in the same hybridgrating profile 59 on the base layer 460. In this embodiment, the densevias 760 are formed in a dense via field 750 adjacent to a surroundingregion of exposed base layer 460. In this embodiment, each dense via 760is square and approximately the same size and shape in this embodiment.In another embodiment, one or more dense vias 760 may be unique in sizeand/or shape. For example, each dense via 760 may be circular, diamond,elliptical, hexagonal, or rectangularly shaped, though the embodiment isnot so limited.

FIG. 8 is an illustration of a further embodiment of a hybrid gratingprofile 59 as part of the wafer 47 in FIG. 1. A fourth reference grating800 is another embodiment of the hybrid grating profile 59 that iscomprised of a plurality of isolated vias 720 located proximate to aplurality of dense vias 760. In this embodiment, a plurality of densevias 760 and a plurality of isolated vias 720 configured in acheckerboard design creates a hybrid grating profile 59. However, theplurality of dense vias 760 and the plurality of isolated vias 720 maybe alternatively oriented in other patterns with a series of dense vias760 configured adjacent to a plurality of isolated vias.

FIG. 9 is a table of lithography simulation data of an isolatedline-space profile and a dense line-space profile. The measurement datain FIG. 9 was compiled by measuring an isolated critical dimension (ICD)separate from a dense critical dimension (DCD) measurement to derive aniso dense bias (Δ_(IB)) where Δ_(IB)=ICD−DCD. A two measurement processis performed according to prior art methods. Each Δ_(IB) value in FIG. 9is a result of two separate measurements, a first measurement for theICD and a second measurement for the DCD. In the table of FIG. 9, a doseof electromagnetic energy measured in milli-Joules per square centimeter(mJ/cm̂2) is applied in a range from 20 to 25 mJ/cm̂2 in increments of1.25 mJ/cm̂2 and a coherence parameter for annular illumination schema(σ_(i)), an optical parameter expressing a ratio of numerical aperturevalues, is varied from 0.6 to 0.78 in increments of 0.045 to form amatrix of measurement data and derived Δ_(IB). In this embodiment, adepth of focus of the optical metrology system 40 was set at zero,meaning that the focus plane was established at the top location 440 ofthe isolated line structure 335 and the comparison line structure ofFIG. 3.

A well designed mask results in a good correlation between realiso-dense bias measured at isolated and dense grating patternsseparately (see FIG. 9) and the iso-dense bias printed with the hybridmask (see FIG. 10).

As an example, for the lithography simulation data in FIG. 9, it may bedesirable to establish a minimal iso-dense bias between the ICD and theDCD. In that case, the minimal iso dense bias would be at a dose of21.25 mJ/cm̂2 at a σ_(i) of 0.735.

FIG. 10 is a table of lithography simulation data of a line-space hybridgrating profile 59, such as the first reference grating 300 of FIG. 3.In this case, the measurement data in FIG. 10 was compiled by a singlemeasurement of a hybrid grating profile 59 to derive an iso dense bias(Δ_(IB)) where Δ_(IB)=ICD−DCD. Each Δ_(IB) value in FIG. 9 is a resultof a single measurement that is capable of deriving a first measurementfor the ICD and a second measurement for the DCD. In the table of FIG.10, a dose measured in milli-Joules per square centimeter (mJ/cm̂2) isapplied in a range from 20 to 25 mJ/cm̂2 in increments of 1.25 mJ/cm̂2 anda coherence parameter (σ_(i)) is varied from 0.6 to 0.78 in incrementsof 0.045 to form a matrix of measurement data and derived Δ_(IB). Inthis embodiment, a depth of focus of the optical metrology system 40 wasset at zero, meaning that the focus plane was established at the toplocation 440 of the isolated line structure 335 and the comparison linestructure of FIG. 3.

As an example, for the simulation data in FIG. 10, it may be desirableto establish a minimal iso dense bias between the ICD and the DCD. Inthat case, the minimal iso dense bias would be at a dose of 21.25 mJ/cm̂2at a σ_(i) of 0.735. Alternatively, it may be desirable to monitor theiso dense bias, for example, by establishing an expected value for aniso dense bias, then monitoring a deviation from the expected value forsubsequent hybrid grating profiles 59 measured by the optical metrologysystem 40. Subsequent wafers 47 with hybrid grating profiles 59 thathave a deviation from an expected value that is equal to or greater thanan established value may be flagged as non-conforming. As a result, aprocess may be monitored using a single measurement that takes intoaccount a plurality of critical dimensions of a grating profile.

FIG. 11 is an exemplary block diagram of an optical metrology system 40coupled to a fabrication cluster 702 configured to provide a fabricationprocess. In one exemplary embodiment, optical metrology system 40 mayinclude a library 710 with a plurality of simulated differencediffraction signals and a plurality of profile parameters associatedwith the plurality of simulated difference diffraction signals.Metrology processor 708 can calculate a simulated approximationdiffraction signal and can compare a measured diffraction signal from astructure fabricated in fabrication cluster 702, adjusted by subtractingthe simulated approximation diffraction signal, to the plurality ofsimulated difference diffraction signals in the library. Fabricationcluster 702 is configured to perform a fabrication process to fabricateone or more elements of a structure on a wafer. In one embodiment, thefabrication process is a lithography exposure process. In anotherembodiment, the fabrication process is a lithography develop process.Other examples of fabrication processes include processes used tofabricate semiconductor devices such as dry etch, chemical mechanicalpolishing, wet etch, chemical vapor deposition, physical vapordeposition, implantation, atomic layer deposition, and coatingprocesses, though the embodiment is not so limited.

When a matching simulated difference diffraction signal is found, theprofile parameters associated with the matching simulated differencediffraction signal in the library are assumed to correspond to theprofile parameters of the actual structure measured by the optical beamreceiver 51. A wireless communications link 704 may be provided to allowthe optical metrology system 40 to communicate with the fabricationcluster 702.

The wireless communication link 704 may be in accordance with specificcommunication standards, such as the Institute of Electrical andElectronics Engineers (IEEE) standards including IEEE 802.11(a),802.11(b), 802.11(g), and/or 802.11(n) standards and/or proposedspecifications for wireless local area networks, although the scope ofthe invention is not limited in this respect as they may also besuitable to transmit and/or receive communications in accordance withother techniques and standards. For more information with respect to theIEEE 802.11, please refer to “IEEE Standards for InformationTechnology—Telecommunications and Information Exchange BetweenSystems”—Local Area Networks—Specific Requirements—Part 11 “Wireless LANMedium Access Control (MAC) and Physical Layer (PHY), ISO/IEC 8802-11:1999” and related amendments/versions.

Alternatively, or in combination with the wireless communications link,a wired communications link 706 may be provided to allow the opticalmetrology system 40 to communication with the fabrication cluster 702.The optical metrology system 40 can transmit digital data to thefabrication cluster 702 via wired communications link 706. The wiredcommunications link 706 may be a physical medium such as an AC powerline, telephone line or other electrical wire, a cable, a copper line,or the like. In one embodiment, the wired communications link 706 may bein accordance with specific communications standards, such as cancommunicate using one of many communication protocols, includingAsynchronous Transfer Mode (ATM), IEEE 802.3 or 802.1, or a collectionof standards defining a physical layer and a media access controlsublayer of a data link layer of wired Ethernet.

FIG. 12 is a flowchart describing one embodiment of a method of using anoptical metrology system 40 to monitor one or more output parametersusing a hybrid grating profile 59, as illustrated in FIG. 1 through FIG.10, from the fabrication cluster 702 and providing feedback to adjustthe output parameters from the fabrication cluster 702. The process maybe initiated (element 810) by forming a grating layer or hybrid gratingprofile 59 comprising a plurality of repeating profiles on a workpiece47 using a fabrication cluster 702, each repeating profile comprising adense region and an isolated region, the dense region including aplurality of features including a comparison line structure 345, theisolated region including an isolated line structure 335. Also, eachrepeating profile is configured in a pattern so that the iso dense biasis within a range determined for the workpiece. The range for the isodense bias may be established in part by the design of the hybridgrating profile 59, for example, by establishing a comparison linestructure width 350 and an isolated line structure width 340 accordingto desired values and/or by modifying one or more measurement parametersof the optical metrology system 40 such as the dose, depth of field, orcoherence parameter. The fabrication cluster 702 may be a single processtool or a plurality of process tools. For example, a fabrication cluster702 may be a single dry etch system as known to one having skill in theart of semiconductor manufacturing. Alternatively, the fabricationcluster 702 may be a plurality of process tools, such as a lithographyscanner combined with a lithography coater/developer.

The workpiece 47 with the grating layer is disposed in an opticalmetrology system 40 in element 820 and the grating layer on theworkpiece 47 is exposed to electromagnetic energy in element 830. Theelectromagnetic energy may be provided by a spectroscopic sourcetypically employed on a scatterometry type optical metrology system 40.One example of an optical metrology system 40 is an ellipsometry-basedoptical measurement and characterization system. In another embodiment,the optical metrology system 40 is a reflectometer or other opticalmetrology device to measure the diffracted beam or spectrum. In oneembodiment, the beam 43 may impinge the hybrid grating profile 59 in aspot size measuring approximately between 20 and 200 microns. In anotherembodiment, the beam 43 may impinge the hybrid grating profile 59 in aspot size measuring approximately between 25 and 45 microns. The shapeof the spot may be circular, elliptical, square, or rectangular, thoughthe embodiment is not so limited.

A diffraction signal is measured from the electromagnetic energydiffracted by the grating layer and an iso-dense bias is determined inelement 840. In element 850, the iso-dense bias and the second iso-densebias are transmitted to the fabrication cluster using the wirelesscommunication link 704 and/or the wired communications link 706. One ormore process parameters and/or equipment settings are adjusted based atleast on the iso-dense bias in element 860.

A plurality of embodiments of method of controlling a fabricationprocess using an iso-dense bias have been described. The foregoingdescription of the embodiments of the invention has been presented forthe purposes of illustration and description. It is not intended to beexhaustive or to limit the invention to the precise forms disclosed.This description and the claims following include terms, such as left,right, top, bottom, over, under, upper, lower, first, second, etc. thatare used for descriptive purposes only and are not to be construed aslimiting. For example, terms designating relative vertical positionrefer to a situation where a device side (or active surface) of aworkpiece 47 or integrated circuit is the “top” surface of thatworkpiece 47; the workpiece 47 may actually be in any orientation sothat a “top” side of a workpiece 47 may be lower than the “bottom” sidein a standard terrestrial frame of reference and still fall within themeaning of the term “top.” The term “on” as used herein (including inthe claims) does not indicate that a first layer “on” a second layer isdirectly on and in immediate contact with the second layer unless suchis specifically stated; there may be a third layer or other structurebetween the first layer and the second layer on the first layer. Theembodiments of a device or article described herein can be manufactured,used, or shipped in a number of positions and orientations.

Persons skilled in the relevant art can appreciate that manymodifications and variations are possible in light of the aboveteaching. Persons skilled in the art will recognize various equivalentcombinations and substitutions for various components shown in theFigures. It is therefore intended that the scope of the invention belimited not by this detailed description, but rather by the claimsappended hereto.

1. A method of controlling a fabrication process using iso dense bias,the method comprising: defining a grating layer, the grating layercomprising a dense area with a plurality of dense features and anisolated area with at least one isolated feature; forming the gratinglayer on a first substrate using a fabrication cluster; providing thegrating layer on the first substrate to a metrology tool; exposing thegrating layer to electromagnetic energy; measuring a first diffractionsignal from the electromagnetic energy diffracted by the grating layerand establishing a first iso-dense bias; forming the grating layer on asecond substrate using the fabrication cluster; providing the gratinglayer on the second substrate to the metrology tool; exposing thegrating layer to electromagnetic energy; measuring a second diffractionsignal from the electromagnetic energy diffracted by the grating layerand establishing a second iso-dense bias; transmitting the firstiso-dense bias and the second iso-dense bias to the fabrication clusterwherein the fabrication cluster was used to create the grating layer onthe first substrate and the second substrate, the fabrication clusterhaving process parameters and equipment settings; and adjusting one ormore process parameters or equipment settings of the fabrication clusterbased at least on the difference between the first iso-dense bias andthe second iso-dense bias.
 2. The method of claim 1, wherein the densefeatures and the isolated feature are formed in a layer on a substrate.3. The method of claim 1, wherein the dense features and the isolatedfeature are formed from a layer on a substrate.
 4. The method of claim1, wherein a spot size for the electromagnetic energy is less than 55microns.
 5. The method of claim 1, wherein the metrology tool is areflectometer or an ellipsometer.
 6. The method of claim 1, wherein theelectromagnetic energy is emitted from a monochromatic source.
 7. Themethod of claim 1, wherein the electromagnetic energy is emitted from aspectroscopic source.
 8. The method of claim 1, wherein the metrologytool is incorporated in the fabrication cluster.
 9. The method of claim1, wherein the fabrication cluster comprises a lithography exposure tooland a coater/developer system.